1. Field of the Invention
The present invention is broadly concerned with methods and apparatus for the processing of preprinted continuous label-bearing webs using laser cutting techniques and employing low-cost, lightweight liners as opposed to the relatively thick and more costly liners conventionally used in the production of die cut label products. More particularly, the invention pertains to such methods and apparatus wherein a preprinted label-bearing web is separated from its liner, laser cut preferably using a plurality of computer controlled laser beams to generate individual cut labels, whereupon the individual labels are reapplied either to the original liner or a secondary liner web. Sensors may also be employed for determining the existence of any gaps or misprinted label images on the web, and to responsively control the laser cutter to prevent cutting of the web at such locations. In this way, only labels meeting customer specifications are actually cut and applied to a liner web as final label product.
2. Description of the Prior Art
Laser cutting of label products is now an accomplished fact. In such systems, a computer controlled laser is employed to cut individual labels from a preprinted, continuous web as opposed to prior techniques making use of cutting dies. Such laser production of labels has many advantages, including higher processing speeds and the possibility of eliminating altogether the use of a supporting liner web.
For example, U.S. Pat. No. 5,421,933 describes a system for laser cutting and applying labels from continuous, preprinted label stock. In this disclosure, the preferred system eliminates the need for a liner web and allows successive cutting, adhesive activation and label application onto products. Another embodiment described in the ""933 patent involves temporary separation of a liner from the image-bearing label web, with laser cutting occurring during such separation. This embodiment is somewhat limited in its applicability, however, owing to the fact that the laser device is incapable of rapidly cutting complex labels. Moreover, the laser cutting area where the liner is separated from the label web must be relatively small, so that the axial height of each label permits the label to bridge the point of laser cutting and the area of reapplication of the label to the liner. Finally, in this design the cutting laser beam impinges directly on the outer printed surface of the label stock. This has been found to present a problem, particularly with more powerful lasers needed for rapid processing. Specifically, direct impingement of the laser beam onto the printed side of the label-bearing web can cause discoloration of the finished labels. Other specific laser cutting systems for label production are disclosed in U.S. Pat. Nos. 5,487,807, 5,679,199, 5,681,412 and 5,624,520.
Generally, the rate-limiting step in the production of laser cut labels using the foregoing systems is the laser cutting step itself. These prior systems used control algorithms and laser devices which were relatively slow, thereby decreasing the overall output rate of finished label product. This is particularly the case with the previously described gap-cutting embodiment of the ""933 patent.
The present overcomes the problems outlined above and provides apparatus and corresponding methods for processing of a preprinted continuous web having printed thereon a plurality of individual, axially spaced apart segments each having a maximum axial dimension. The method involves providing a continuous, composite web including the preprinted web (having a printed surface bearing axially spaced images or segments and an opposed adhesive-bearing face) and a first liner web (having a release coating on both opposed surfaces thereof). The liner and preprinted webs are initially separated with the preprinted web being passed through a laser cutting station where at least one laser beam is directed against the preprinted web for cutting individual labels or segments therefrom, with the liner web being wound on a collection spindle. After the laser cutting operation, the individual preprinted segments are conveyed along a path of travel substantially longer than the maximum axial dimensions of the segments to an attachment station where the segments are sequentially attached to a second liner web.
In practice, the cut segments are conveyed between the cutting and attachment stations using a supporting conveyor such as an apertured vacuum belt. Furthermore, the preprinted web is preferably oriented in the cutting station and conveyor so that the adhesive-bearing face thereof is proximal to the laser device, i.e., the laser beam(s) impinge upon the adhesive-bearing face rather than the printed face. The cut segments are conveyed in this orientation to the attachment station where they are applied to a liner web. This liner web may be the original web forming a part of the composite web, or a separate liner web. The preferred control of the invention allows the laser beam(s) to be controlled in such a way that the preprinted web is moved at a substantially constant speed through the cutting station, This compares with certain prior art systems where, in order to accommodate complex label designs, it was necessary to speed up or slow down the web speed through the cutting station.
In preferred embodiments, the web processing apparatus of the invention includes a sensor positioned upstream of the web cutting station which observes the printed images as they move into the cutting, station. This sensor is coupled through a controller to the laser device. If missing or misprinted segment images are detected, an appropriate control signal is sent to the laser device to prevent cutting of the preprinted web at the region of the missing or misprinted images. Similarly, in embodiments using a second liner web, another sensor is located upstream of the attachment station which is connected via the controller to the second liner web for the cut segments. Thus, if this sensor detects an absence of cut segments (which would occur in the event of operation of the first sensor as described), then movement of the second liner web is terminated or otherwise adjusted so that properly printed segments are evenly spaced on the final label product web.
A prime advantage of the present invention is that use can be made of relatively thin, inexpensive liner webs, as opposed to the heavier webs typically required in label die cutting systems. Moreover, where separate liner webs are employed, it is only necessary to purchase one additional liner web. During each processing run, a fresh liner web is collected in roll form, and can be used as the cut segment support liner web for the next run.